In the field of semiconductor devices, devices have been made more and more compact and thinner and thinner, and as such a semiconductor device, there is a device as shown in FIG. 5, for example. FIG. 5 shows an image sensor 80 as an example of a semiconductor device, and this image sensor 80 has a configuration in which the underside of a silicon substrate 81 and the top surface of a glass substrate 95 are bonded together by an adhesive 96.
The underside of the silicon substrate 81 has an image capturing section 82 and pad electrodes 83 electrically connected to the image capturing section 82 formed therein, and the surface thereof has connecting terminals 84 and wiring films 85 electrically connected to the connecting terminals 84 formed therein. Further, the silicon substrate 81 has through electrodes 86 formed therein, the through electrodes 86 connecting the pad electrodes 83 and the wiring films 85 electrically.
The through electrodes 86 are formed by filling holes 87, which are formed in the surface of the silicon substrate 81 so that the top surfaces of the pad electrodes 83 are exposed, with an electrically conductive material, and an oxide film (insulation film) 88 is formed between the inner peripheral surfaces of the holes 87 and the outer peripheral surfaces of the through electrodes 86 and on the surface of the substrate 81 excluding the portions of the holes 87. Further, on the oxide film 88, the wiring films 85 and a passivation film 89 are formed.
In this image sensor 80, a series of processings for forming the through electrodes 86 in the silicon substrate 81 include a processing of forming the holes 87 and the oxide film 88. The holes 87 and the oxide film 88 are conventionally formed in such a way as shown in FIG. 6, for example (see the Japanese Unexamined Patent Application Publication No. 2009-158862).
That is, initially, a first step of forming a resist film 90 having a mask pattern of a predetermined shape on the surface of the silicon substrate 81 (see FIG. 6(a)) is performed and then a second step of etching the surface of the silicon substrate 81 using the resist film 90 as mask (see FIG. 6(b)) is performed. In the second step, plasma is generated from an etching gas and the silicon substrate 81 is etched until the top surfaces of the pad electrodes 83 are exposed. Thereby, the holes 87 are formed in the surface of the silicon substrate 81.
Subsequently, a third step of removing the resist film 90 from the top surface of the silicon substrate 81 (see FIG. 6(c)) is performed and then a fourth step of forming the oxide film 88 on the surface of the silicon substrate 81 (see FIG. 6(d)) is performed. In the fourth step, plasma is generated from a deposition gas and the oxide film 88 is formed on the surface of the silicon substrate 81 including the side walls and the bottom surfaces of the holes 87 (the top surfaces of the pad electrodes 83).
Thereafter, a fifth step of forming a resist film 91 having a mask pattern of a predetermined shape on the oxide film 88 formed on the surface of the silicon substrate 81 excluding the portions of the holes 87 (hereinafter, referred to as “the top surface of the silicon substrate 81”) (see FIG. 6(e)) is performed and then a sixth step of removing the oxide film 88 formed on the bottom surfaces of the holes 87 (the surfaces of the pad electrodes 83) by etching the oxide film 88 using the resist film 91 as mask (see FIG. 6(f)) is performed. In the sixth step, plasma is generated from an etching gas and the oxide film 88 is etched until the surfaces of the pad electrodes 83 are exposed.
Then, a seventh step of removing the resist film 91 from the surface of the oxide film 88 (see FIG. 6(g)) is performed. Thus, the holes 87 are formed in the silicon substrate 81 and the oxide film 88 is formed on the top surface of the silicon substrate 81 and on the side walls of the holes 87. Thereafter, the holes 87 are filled with an electrically conductive material and the wiring films 85 and the passivation film 89 are formed on the top surface of the oxide film 88, thereby forming the through electrodes 86.
However, forming the holes 87 and the oxide film 88 in this way causes the following problems. That is, in order to form the oxide film 88 on the top surface of the silicon substrate 81 and on the side walls of the holes 87, it is necessary to remove the oxide film 88 formed on the bottom surfaces of the holes 87 after temporarily forming the oxide film 88 on the entire surface of the silicon substrate 81 including the side walls and the bottom surfaces of the holes 87. However, performing the step of forming the resist film 91 for removing the oxide film 88 on the bottom surfaces of the holes 87 (the fifth step), the step of removing the oxide film 88 formed on the bottom surfaces of the holes 87 by etching (the sixth step) and the step of removing the resist film 91 (the seventh step) successively as described above for removing the oxide film 88 formed on the bottom surfaces requires many steps for removing the oxide film 88 formed on the bottom surfaces of the holes 87, which leads to high costs and lengthens the tact time in device production. Further, the increase of the number of steps can be a factor in the decline of the yield due to a trouble caused by the devices.
Therefore, there is taken a measure in which, when forming the oxide film 88 on the surface of the silicon substrate 81 including the side walls of the holes 87 and the bottom surfaces of the holes 87 (the surfaces of the pad electrodes 83) in the fourth step, as shown in FIG. 7(d), the oxide film 88 is formed so that it has a larger film thickness on the top surface of the silicon substrate 81 than on the bottom surfaces of the holes 87, and in the fifth step following this forth step, as shown in FIG. 7(e), the surface of the silicon substrate 81 (oxide film 88) is anisotropically etched so that the oxide film 88 formed on the bottom surfaces of the holes 87 is removed and the surfaces of the pad electrodes 83 are therefore exposed.
Forming the oxide film 88 so that it has a larger film thickness on the top surface of the silicon substrate 81 as described above makes it possible to remove the oxide film 88 formed on the bottom surfaces of the holes 87 with the oxide film 88 formed on the top surface of the silicon substrate 81 remaining at the time of anisotropic etching.
Therefore, since it is possible to omit the step of forming the resist film 91 for removing the oxide film 88 formed on the bottom surfaces of the holes 87 (the step shown in FIG. 6(e)) and the step of removing the resist film 91 (the step shown in FIG. 6(g)), which is performed after removing the oxide film 88 formed on the bottom surfaces of the holes 87, the oxide film 88 formed on the bottom surfaces of the holes 87 can be efficiently removed, and the reduction of costs can be achieved by the shortening of the process. Further, it is possible to eliminate the possibility that the yield declines due to a trouble caused by the devices. It is noted that the FIGS. 7(a) to 7(c) in FIG. 7 correspond to FIG. 6(a) (first step), FIG. 6(b) (second step) and FIG. 6(c) (third step), respectively.